The present invention relates to a process for preparing a synthetic resin powder having an improved blocking resistance, and more particularly to a process for improving blocking resistance of graft copolymers containing a rubber as a trunk polymer which are intended to incorporate into vinyl chloride resins in order to improve the properties of the vinyl chloride resins.
Improvement in powder properties of synthetic resins, particularly bulk density and blocking resistance of the powders, has hitherto been made in various manners. For instance, in Japanese Patent Publication Kokai No. 57-59992 it is proposed to coagulate a latex of a graft copolymer in a gaseous phase. This method improves the blocking resistance of the graft copolymer powder to a great degree.
Various graft copolymers wherein monomers are graft-polymerized onto an elastomer trunk, have been proposed and used as modifiers for vinyl chloride resins, particularly as impact modifiers, e.g. ABS resin, MBS resin and MABS resin. These graft copolymers used as modifiers for vinyl chloride resins are not satisfactory in blocking resistance.
In recent years, improvement in powder properties of synthetic resins such as blocking resistance has been increasingly demanded with application of automatic gaging to powders and change of transportation lines to large scale. Accordingly, further improvement of powder properties has been investigated.
I For instance, Japanese Patent Publication Kokoku No. 58-48584 proposes to improve the powder properties of a conventional graft copolymer containing a large quantity of a rubber, such as impact modifier for vinyl chloride resins, by mixing it with a graft copolymer having a low content of a rubber in the form of a slurry. However, the effect of improving the powder properties of this method is small since the graft copolymer added for the improvement of powder properties contains a rubber though the content is low. This Japanese publication also discloses in Comparative Example 3 to incorporate a polymer containing no rubber component, namely a copolymer of 55% by weight of methyl methacrylate and 45% by weight of styrene, into a conventional graft copolymer known as a modifier. In that case, powder properties of the conventional graft copolymer are improved, but the effect of the improvement is small like in the case of using a graft copolymer having a low rubber content as an improving agent. Moreover, it is disclosed that a large number of fish eyes generate in molded articles prepared from a vinyl chloride resin to which the thus treated modifier is incorporated, or the impact resistance of the molded articles is remarkably decreased.
Japanese Patent Publication Kokai No. 58-1742 discloses, improving the powder properties of a graft copolymer having a high content of a rubber known as a modifier by mixing the slurry of the graft copolymer with an emulsion of a hard non-elastomeric polymer. Japanese Patent Publication Kokai No. 4-300947 discloses improving the powder properties of a graft copolymer having a high content of a rubber known as a modifier by mixing a slurry of the graft copolymer with a slurry of a hard polymer containing methyl methacrylate as an essential component and containing 5 to 30% by weight of an acrylic acid ester prepared by a multi-stage polymerization. However, these methods have the disadvantage that when a large amount of an acrylic acid ester is used, the effect of improving the blocking resistance of the graft copolymer is small and when the amount is small, a large number of fish eyes generate in molded articles of vinyl chloride resins, thus these two important properties are not satisfied simultaneously.
There has been strongly demanded a modifier for vinyl chloride resins which has an improved blocking resistance and which can be incorporated into the vinyl chloride resins to give a vinyl chloride resin composition having excellent impact resistance and transparency without generating fish eyes in molded articles of the vinyl chloride resins.
It is an object of the present invention to provide a graft copolymer having an improved blocking resistance which can be incorporated into vinyl chloride resins is a modifier to give a vinyl chloride resin composition having excellent impact resistance and transparency without generating fish eyes in the molded articles prepared therefrom.
A further object of the present invention is to provide a process for improving the powder properties particularly the blocking resistance, of graft copolymers containing a rubber as a trunk polymer, which have been known as modifiers, particularly impact modifiers, for vinyl chloride resins or the like, without causing problems in generation of a large number of fish eyes, decrease of the effect of improving the impact resistance that the modifiers originally possess, and decrease of the transparency of molded articles of the vinyl chloride resins on the like.
These and other objects of the present invention will become apparent from the description hereinafter.